[cppyy] fix: aliasing of TemplateProxy

bindings/pyroot/cppyy/CPyCppyy/src/TemplateProxy.cxx

@@ -231,9 +231,7 @@ PyObject* TemplateProxy::Instantiate(const std::string& fname,
         if (pyol && !bIsCppOL && !TemplateProxy_Check(pyol)) {
         // unknown object ... leave well alone
             Py_DECREF(pyol);
-            Py_DECREF(pycachename);
-            Py_DECREF(dct);
-            return nullptr;
+            pyol = nullptr;
         }
 
     // find the full name if the requested one was partial

bindings/pyroot/cppyy/cppyy/test/test_templates.py

@@ -1,4 +1,4 @@
 import pytest, os
 from pytest import mark, raises
 from support import setup_make, pylong, IS_WINDOWS
 
@@ -23,8 +23,8 @@
     def test01_template_member_functions(self):
         """Template member functions lookup and calls"""
 
         import cppyy
         import sys
 
         m = cppyy.gbl.MyTemplatedMethodClass()
 
@@ -40,7 +40,7 @@
         if sys.hexversion >= 0x3000000:
             targ = 'long'
         else:
             targ = long
         assert m.get_size[targ]()     == m.get_long_size()
 
         import ctypes
@@ -104,15 +104,15 @@
         from cppyy.gbl.std import vector
         # float in, float out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<float>']
         assert type(ggsr(vector['float']([0.5])).m_retval) == float
         assert ggsr(vector['float']([0.5])).m_retval == 0.5
         # int in, float out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<int>']
         assert type(ggsr(vector['int']([5])).m_retval) == float
         assert ggsr(vector['int']([5])).m_retval == 5.
         # float in, int out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<float>, int']
         assert type(ggsr(vector['float']([0.3])).m_retval) == int
         assert ggsr(vector['float']([0.3])).m_retval == 0
         # int in, int out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<int>, int']
@@ -1206,6 +1206,27 @@
 
         a = ns.S(1, 2)
         assert a.m_a == 1
+
+    def test37_deleted_alias_of_template_proxy(self):
+        """Alias TemplateProxy and set None to orginal"""
+        import cppyy
+
+        cppyy.cppdef(r"""
+            struct PyA {
+                template <typename T>
+                T get() { return (T)-1; }
+            };
+        """)
+
+        PyA = cppyy.gbl.PyA
+        PyA.getter = PyA.get
+
+        assert PyA().get["int"]() == -1
+        assert PyA().getter["int"]() == -1
+
+        PyA.get = None
+
+        assert PyA().getter["float"]() == -1.0
 
 
 class TestTEMPLATED_TYPEDEFS: